Method of manufacturing whisker electrodes



Nov. 2, 1954 A. M. GUREWITSCH ETAL 2,693,022

METHOD OF MANUFACTURING WHISKER ELECTRODES I Filed Oct. 6, 1950 V///////% w m Fig.1.

United States Patent C) METHOD OF MANUFACTURING WHISKER ELECTRODES Anatole M. Gurewitsch and William C. Dunlap, Jr}, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application October 6, 1950, Serial No. 188,766

2 Claims. (Cl. 29-4555) This invention is for a method of producing a sharp point on an end of a fine wire and also relates to an improvement in whisker electrodes as utilized in asymmetrically conductive devices.

Asymmetrical conducting devices employ one or more whisker electrodes which are generally very fine wires sharpened to a point at one end. in these devices, such, for example, as transistors, this whisker must be mounted so that it is in contact with a crystal-like member. Because the whisker is of the order of 1 mil in thlckness, it is diflicult to sharpen it to a point and also to mount it.

An object of this invention is to provide a new and improved method for establishing a pointed end on a line wire.

Another object of this invention is to provide a new and improved method for mounting a whisker electrode in an asymmetrically conductive device.

A further object of this invention is to provide a new and improved method suitable for the mass production of whisker electrodes applicable for mounting in a symmetrically conductive devices.

A still further object of this invention is to provide a new and improved electrode suitable for use as the point electrode in asymmetrically conductive devices.

A still further object of this invention is to provide new and improved means for mounting a whisker electrode in an asymmetrically conductive device.

In the attainment of the foregoing objects there is providcd a length of fine wire constructed of a material making it suitable for use as a whisker or point electrode. This wire is coated by a relatively thick metallic layer and then cut at an angle to the longitudinal axis thereof into a plurality of sections. An end of the metallic coating on each of these sections is then dissolved in an acid exposing a sharp end of the inner, fine wire. The other end of the coating which has not been dissolved provides a dependable and practical means by which the wire whisker may be mounted in an asymmetrically conducting device.

For further objects and advantages and for a better understanding of this invention, attention is now directed to the following description and accompanying drawings and also to the appended claims. In the drawing Figs. 1 and 2 illustrate in cross-sectional view asymmetrically conductive devices employing different embodiments of this invention.

In Fig. 1 a fine conducting wire 1 pointed at one end is supported in a thick metallic coating or layer 2. Coating 2 is rigidly mounted within one end of a tube 3 constructed of an insulating material. The pointed end of wire 1 contacts the upper surface of an asymmetrically conductive material 4 which rests on a conducting block 5. Block 5 has an outer shape substantially conforming to the shape of the inner wall of tube 3. A resilient member which is shown in the drawing as a spring 6 is located between block 5 and a lip on the bottom portion of tube 3 to provide the necessary force required to insure good contact between wire 1 and member 4. An electrical conductor 7 which is connected at one end of block 5 extends from within the tube.

The asymmetrically conductive device in Fig. 2 is similar to that of Fig. 1 except that the force providing good contact between a whisker electrode 8 and asymmetrically conducting member 4 is established by locating asymmetrically conducting material 4 on a conducting block 9 which is cemented to the inner surface of tube 3 and making whisker 8 substantially S-shaped.

This invention is more particularly concerned with ICC ,the construction of the whisker and the metallic coating in. which. it is located. To provide a whisker which is securely mounted within a thick metallic coating and which has-a sharp point at one end, thefollowing method may be used.

The thin conducting wire suitable for use as a whisker electrode isfirst coated with a thick metallic layer. This may be done in a number of ways. One method is to buildup .a deposit of a desirable thickness by an electroplating process. Another method is to place the thin wire in a metallic tube which is subsequently swaged" to the desired diameter. A still further method is to solder the thin wire within a metallic tube which is al ready of the desired outside diameter.

Having thus coated the fine wire with a metallic layer by any convenient means, a sturdy wire is provided which may be handled with facility without undue care. The thick metal coating thus protects the thin wire from rupture during normal manufacturing operations of an asymmetrically conducting device. The thin wire and the thick coating are cut at an angle to the longitudinal axis of the wire into sections. Each of these sections is to be used as a whisker electrode and a support therefor. The coating at one end of the section is dissolved with an acid; thereby leaving the sharply pointed fine wire exposed at one end of the section. Other metals and other acids may, of course, be used, but if platinum or tungsten is used for the fine wire whisker electrode it may be convenient to coat the wire with a thick layer of cop-v per which may be dissolved away from the fine wire by nitric acid.

The end of the section having the thick metallic coating provides a very suitable mount for the fine whisker in a device in which it is to be utilized. This method of producing a sharp pointed whisker electrode has many advantages over prior art methods, especially where mass production thereof is desired. Some of the advantages are that a sharp point may easily be obtained on the fine wire since the heavy metal envelope provides a mechanical support for the weak. thin wire while it is being cut and the presence of a thick metal rod close to the point of contact of the crystal in asymmetrically conductive devices increases the heat conductivity of the electrode thereby increasing the power rating thereof. Another advantage of this type electrode is that the construction obviates the necessity of welding the whisker to a metal lead when the whisker is utilized in an asymmetrically conductive device. When employed in asymmetrically conductive devices the cylindrical shape of the mount, which of course is the thick metallic coating on the fine wire. makes possible a simplified design. For example, as shown in the two figures of the drawing, the whisker assembly may simply be inserted into a cylindrical sleeve made of insulating material to contact a crystal which is located in this sleeve. This design is particularly suited for making contact to small spheres of ermanium diodes.

This type whisker electrode and accompanying mount also finds application in high frequency apparatus. In such applications the exposed portion of the fine wire is extremely short to materially reduce the inductance thereof. As is well known in the art, this inductance is of ma or concern in rectifying crystals operated in the thousand megacycle range.

While this invention has been described by particular embodn'nents thereof, it will be understood that those skilled in the art may make many changes and modifications without departing from this invention. Therefore, by the appended claims it is intended to cover all such changes and modifications which fall within the true spirit and scope of this invention.

at we claim as new and desire to secure by Letters Patent of the United States is:

1. A method for establishing a sharp point at the end of a fine single strand Wire comprising the steps of surrounding the fine wire with a thick metallic layer, sever- 1ng the layer and the fine wire at an acute angle to the longitudinal axis of said fine wire, and dissolving the metallic coating away from the portion of the fine wire WhlCh 1s severed at an acute angle thereby exposing a sharply pointed end of the wire, the remaining undis' 3 solved portion of the coating forming a conductive terminal portion.

2. A method for manufacturing a whisker electrode suitable for use in asymmetrically conductive devices comprising the steps of coating a thin single strand conducting wire with a thick metallic layer, cutting the layer and the wire at an angle with the longitudinal axis of said Wire so as to form an off-center point on the severed ends of said wire, and dissolving the thick metallic coating away from said severed ends of the wire thereby exposing the sharply pointed ends of the wire without disturbing the opposite ends thereof which are securely mounted in the thick metallic coating at the other end of each wire to form a conductive terminal portion for said whisker electrode.

Number UNITED STATES PATENTS Name Date Steenstrup Oct. 8, Ryan Feb. 17, Everett Dec. 20, Everett Nov. 26, Brickman Apr. 12, Ehrhardt Oct. 21, Pfann Nov. 4, Durst I an. 27, Sirp Aug. 10, Barnes June 20, 

